This invention is converned with techniques for determining the difference between two optical images.
Real-time image processing is becoming an area of great interest to robotics and artificial intelligence. A clear advantage to the optical approach for these applications is the capability of parallel processing. Additional areas of application include industrial quality assurance, optical logic gates, and the detection of motion in a scene.
In principle, coherent image subtraction and addition can be achieved with an interferometer, such as the Mach-Zender or Michelson configurations. Image subtraction is accomplished with an interferometer by destructive interference, which requires that the phases of the illuminating beams be 180.degree. out of phase throughout the two dimensional region within which the images overlap. In practice, however, the overlapped image intensity tends to drift between the extrema because of phase fluctuations due to ambient air currents and thermal drift. Perfect alignment of the interferometer is another problem because such interferometers are extremely sensitive to misalignment.
Therefore, a need has developed in the art for an interferometric image subtraction scheme which is self-aligned and is independent of the optical path length of the interferometer arms.